Controller for hybrid vehicle

ABSTRACT

There is provided a controller for a hybrid vehicle which can improve fuel consumption performance and driveability. 
     A controller for a hybrid vehicle which can run in an EV drive mode in which an electric motor 101 is driven by electric power of a battery 113 only and a series drive mode in which the electric motor 101 is driven by electric power generated by a generator 107 using power of an engine 109 includes a demanded driving force calculation unit, a demanded electric power calculation unit, an available uppermost outputting value setting unit and an engine starting determination unit. The engine starting determination unit starts the engine 109 so that the vehicle runs in the series drive mode when the demanded electric power demanded of the electric motor 101 exceeds the available uppermost outputting value.

TECHNICAL FIELD

The present invention relates to a controller for a hybrid vehicle.

BACKGROUND ART

A hybrid vehicle can run on plural energy sources such as electric powerand fuel and also can run on various drive modes depending upon energysources used. As drive modes of a hybrid vehicle, there are, forexample, an EV drive mode in which the hybrid vehicle runs by driving anelectric motor by electric power of a battery only, a series drive modein which the hybrid vehicle. runs by driving the electric motor byelectric power generated by a generator using power of an engine and anengine drive mode in which the hybrid vehicle runs by driving directlydrive wheels by the engine. For example, Patent Literature I describes ahybrid vehicle which changes drive modes based on demanded torque whichis necessary for propulsion of the vehicle.

Related Art Literature

Patent Literature

Patent Literature 1: JP-H09-224304-A

Outline of the Invention Problems to be Solved by the Invention

In the hybrid vehicle described in Patent Literature 1, as the torquerequirement increases, the drive modes are changed from a drive by theelectric motor alone (the EV drive mode) to a drive by the engine alone(the engine drive mode). When drive wheels are directly driven by theengine, however, a gear ratio to be set is limited, and therefore, theremay be a situation in which it is difficult to run the engine at anoperation point which provides good fuel economy. In view of thesefacts, it is desirable that the drive mode is changed from the EV drivemode to the series drive mode in which the operation point can freely beset.

Additionally, when the drive modes are changed over based on thedemanded torque which is necessary for propulsion of the vehicle, the^(.)vehicle runs in the EV drive mode although a battery cannot outputdemanded electric power which corresponds to the demanded torquedepending upon conditions such as the state-of-charge (SOC) andtemperature of the battery. Therefore, there are fears that thedriveability is deteriorated, In addition, as this occurs, there arefears that the battery is discharged excessively.

The invention has been made in view of the problems, and an objectthereof is to provide a controller for a hybrid vehicle which canimprove the fuel economy and the drivability of the hybrid vehicle.

Means for Solving the Problems

Claim 1 provides a controller for a hybrid vehicle,

the vehicle including

-   -   an engine (e.g., an engine 109 in embodiment),    -   an electric motor (e.g., an electric motor 101 in embodiment),    -   a generator (e.g., a generator 107 in embodiment) for generating        electric power by power of the engine, and    -   a battery (e.g., a battery 113 in embodiment) for storing        electric power generated by the electric motor or the generator        and supplying the electric power to the electric motor,

the vehicle being able to run in

-   -   an EN drive mode in which the electric motor is driven by        electric power of the battery only and    -   a series drive mode in which the electric motor is driven by        electric power generated by the generator using power of the        engine,

the controller including

-   -   a demanded driving force calculation unit (e.g., a management        ECU 119 in embodiment) for calculating a demanded driving force        for the electric motor based on vehicle speed and accelerator        pedal opening,    -   a demanded electric power calculation unit (e.g., the management        ECU 119 in embodiment) for calculating a demanded electric power        based on the demanded driving force and a revolution speed of        the electric motor,    -   an available uppermost outputting value setting unit the        management ECU 119 in embodiment) for setting an available        uppermost outputting value (e.g,, an available uppermost        outputting value P_(U) in embodiment) for the battery based on        the conditions of the battery, and    -   an engine starting determination unit (e.g., the management ECU        119 in embodiment) for determining on the starting of the engine        based on the demanded electric power,

wherein the engine starting determination unit starts the engine so thatthe vehicle runs in the series drive mode when the demanded electricpower exceeds the available uppermost outputting value.

Claim 2 provides, based on Claim 1, the controller,

wherein the series drive mode includes a battery input/output zero modein which only electric power corresponding to the demanded electricpower is generated by the generator for supply to the electric motor,

wherein the controller further includes a set value setting unit (e.g.,the management ECU 119 in embodiment) for setting a set value (e.g., afuel-consumption-reducing output upper limit value P_(I), in embodiment)based on the conditions of the battery,

wherein the set value is a smaller value than the available uppermostoutputting value and is an upper limit value for an output whichsatisfies {(Loss generated when running in EV drive mode)+(Lossgenerated when generating electric power corresponding to electric powerconsumed in EV drive mode)} <(Loss generated in battery input/outputzero mode), and

wherein the engine starting determination unit starts the engine inaccordance with the running conditions of the vehicle so as to cause thevehicle to run in the series drive mode when the demanded electric poweris equal to or larger than the set value and is equal to or smaller thanthe available uppermost outputting value.

Claim 3 provides, based on claim 2, the controller,

wherein the available uppermost outputting value and the set value areset based on the state-of-charge of the battery or the temperature ofthe battery.

Claim 4 provides, based on claim 2, the controller,

wherein the available uppermost outputting value and the set value areset based on a smaller value of values which are calculated based on thestate-of-charge of the battery and the temperature of the battery.

Claim 5 provides, based on any one of claims 2 to 4, the controller,

wherein the available uppermost outputting value and the set value areset smaller as the state-of-charge of the battery becomes smaller.

Claim 6 provides, based on any one of claims 2 to 5, the controller,

wherein the available uppermost outputting value and the set value areset smaller as the temperature of the battery becomes smaller.

Claim 7 provides, based on any one of claims 2 to 6, the controller,further including

-   -   a first fitness calculation unit (e.g., the management ECU 119        in embodiment) for calculating a first fitness between the        available uppermost outputting value and the set value by        executing a fuzzy reasoning from a first membership function        which is set with respect to demanded electric power,    -   a second fitness calculation unit (e.g., the management ECU 119        in embodiment) for calculating a second fitness by executing a        fuzzy reasoning from a second membership function which is set        with respect to variation in accelerator pedal opening, and    -   a degree-of-start-demand calculation unit (e.g., the management        ECU 119 in embodiment) for calculating a degree of start demand        for the engine based on the first fitness and the second        fitness,

wherein the engine starting determination unit starts the engine andcauses the vehicle to run in the series drive mode when an integralvalue obtained by integrating the degree of start demand surpasses apredetermined value, with the demanded electric power being equal to orlarger than the set value and being equal to or smaller than theavailable uppermost outputting value.

Claim 8 provides, based on claim 7, the controller,

wherein the first membership function is corrected in accordance withthe temperature of a coolant of the engine.

Claim 9 provides, based on claim 7 or 8, the controller,

wherein the first membership function is corrected in accordance withenergy which is consumed by an auxiliary (e.g., an auxiliary 117 inembodiment).

Claim 10 provides, based on any one of claims 7 to 9, the controller,further including

an intention-to-accelerate determination unit (e.g., the management ECU119 in embodiment) for determining on a driver's intention toaccelerate,

wherein the second membership function is positively corrected when theintention-to-accelerate determination unit determines that the driver'sintention to accelerate is high, whereas the second membership functionis corrected negatively when the intention-to-accelerate determinationunit determines that the driver's intention to accelerate is low,

Claim 11 provides, based on any one of claims 2 to 10, the controller,

wherein the vehicle can run in an engine drive mode in which drivewheels are driven by power of the engine by engaging a clutch (e.g,, aclutch 115 in embodiment) which is provided between the engine and theelectric motor, wherein the controller further includes a clutchengaging/disengaging unit (e.g,, the management ECU 119 in embodiment)for engaging and disengaging the clutch, and

wherein the clutch engaging/disengaging unit engages the clutch tochange the drive modes from the series drive mode to the engine drivemode when a loss generated in the series drive mode is larger than aloss generated in the engine drive mode.

Advantages of the Invention

According to claim 1, the engine is started when the demanded electricpower demanded of the electric motor surpasses the available uppermostoutputting value which is set in accordance with the conditions of thebattery. Consequently, not only can a desired demanded electric power besecured, but also the over change of the battery can be prevented.

According to claim 2, the set value is set which is the maximum. valueof the demanded electric power with which the fuel consumption resultingwhen the vehicle runs in the EV drive mode is improved better than thefuel consumption resulting when the vehicle runs in the batteryinput/output zero mode, and it is determined based on the set valuewhether or not the engine is started. Therefore, the fuel consumptioncan be improved further. In addition, the set value is set based on theconditions of the battery, and therefore, the over charge of the batterycan be prevented. In addition, when the demanded electric power demandedof the electric motor is somewhere between the set value and theavailable uppermost outputting value, it is determined based on therunning conditions of the vehicle whether or not the engine is started.Therefore, the engine can be started at suitable timing for the runningconditions of the vehicle, thereby making it possible to prevent theperformance of unnecessary operations.

According to claims 3 to 6, it is considered that the electric powerthat can be outputted is reduced depending upon the SOC and temperatureof the battery. Therefore, the demanded electric power can be ensured bystarting the engine earlier to generate electric power.

According to claim 7, it is determined by executing the fuzzy reasoningbased on the demanded electric power demanded of the electric motor andthe driver's intention to accelerate whether or not the engine isstarted. Therefore, there is no fear that the lack of driving force iscaused by the poor output of the battery, and the unnecessary operationof the engine is obviated, Additionally, the continuity of a runningcondition of the vehicle can be determined by integrating the degree ofengine start demand, and therefore, the unnecessary operation of theengine is obviated. By so doing, a more accurate control reflecting theintention of the driver can be performed.

According to claim 8, the temperature of the coolant of the engine istaken into consideration, and therefore, the determination on whether ornot the engine is started can be made in accordance with the temperatureof the coolant of the engine, thereby making it possible to prevent theunnecessary operation of the engine.

According to claim 9, the consumed energy by the auxiliary is taken intoconsideration, and therefore, the demanded electric power can be ensuredby starting the engine earlier to generate electric power, therebymaking it possible to prevent the over charge of the battery.

According to claim 10, the intention of the driver is taken intoconsideration, and therefore, not only can the drivability be improved,but also the fuel consumption can be improved further.

According to claim 11, the drive mode can quickly be changed from theseries drive mode to the engine drive mode when the loss in the enginedrive mode is determined to be less, and therefore, the fuel consumptioncan be improved further,

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a hybrid vehicle which utilizes a controller of anembodiment.

FIG. 2 shows a detailed configuration of the controller for a hybridvehicle.

FIG. 3 shows a detailed configuration of an MOT demanded electric powercalculation block shown in FIG. 2.

FIG. 4 shows a detailed configuration of an ENG-GEN control block shownin FIG. 2.

FIG. 5 shows a detailed configuration of an ENG start determinationblock shown in FIG. 2.

FIG. 6 shows a drive mode fitness estimation.

FIG. 7 shows an available uppermost outputting value and afuel-consumption-reducing output upper limit value.

FIG. 8 shows an intention-to-accelerate estimation.

FIG. 9 shows a detailed configuration of a fuzzy determination blockshown in FIG. 5.

FIG. 10 shows operations of the controller for a hybrid vehicleaccording to the embodiment.

FIG. 11 shows operations of an engine starting determination.

FIG. 12 shows operations of a fuzzy determination.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be described byreference to the accompanying drawings. Note that the drawings are to beseen in a direction in which reference numerals look properly.

An HEV (Hybrid Electrical Vehicle) includes an electric motor and anengine and runs by driving force of the electric motor or the enginedepending, upon the running conditions of the vehicle. FIG. 1 shows aninternal configuration of an HEY (hereinafter, referred to simply as a“vehicle”) of the embodiment. As shown in FIG. 1, the vehicle 1 of theembodiment includes left and right drive wheels DW, DW, an electricmotor (MOT) 101, a first inverter (1^(st) INV) 103, a second inverter(2^(nd) INV) 105, a generator ((lEN) 107, an engine (ENG) 109, abidirectional voltage converter (VCU) (hereinafter, referred to simplyas a “converter”) 111, a battery (BATT) 113, a lockup clutch(hereinafter, referred to simply as a “clutch”) 115, an auxiliary(ACCESSORY) 117, a management ECU (MG ECU) 119, a motor ECU (MOT ECU)121, a battery ECU (BATT ECU) 123, an engine ECU (ENG ECU) 125, and agenerator ECU (GEN ECU) 127.

The electric motor 101 is, for example, a three-phase alternatingcurrent motor. The electric motor 101 generates power (torque) necessaryto run the vehicle. Torque generated in the electric motor 101 istransmitted to the drive wheels DW, DW. When a driving force istransmitted to the electric motor 101 side from the drive wheels DW. DWvia drive shafts at the time of deceleration of the vehicle, theelectric motor 101 functions as a generator to generate a so-calledregenerative braking force and recovers the kinetic energy of thevehicle as electric energy (regenerative energy) to thereby charge thebattery 113. The motor ECU 121 controls the operation and conditions ofthe electric motor 101 in response to an instruction from the managementECU 119.

The multi-cylinder internal combustion engine (hereinafter, referred tosimply as the “engine”) 109 drives the generator 107 to generateelectric power by the power of the engine 109 with the clutch 115disengaged, The engine 109 generates power (torque) necessary to run thevehicle with the clutch 115 engaged. With the clutch 115 engaged, thetorque generated in the engine 109 is transmitted to the drive wheelsDW, DW via the generator 107 and the clutch 115, The engine ECU 125controls the start and stop and revolution speed of the engine 109 inresponse to an instruction from the management ECU 119.

The generator 107 is driven to generate electric power by the engine109. An alternating current voltage generated in the generator 107 isconverted into a direct current voltage by the second inverter 105. Thedirect current voltage converted by the second inverter 105 is droppedby the converter 111 and is then stored in the battery 113 or isconverted into an alternating current voltage via the first inverter 103to thereafter be supplied to the electric motor 101. The generator ECU127 controls the revolution speed of the generator 107 and the amount ofelectric power generated by the generator 107 in response to aninstruction, from the management ECU 119.

The battery 113 has plural battery cells which are connected in seriesand supplies a high voltage of 100 to 200V for example. The voltage ofthe battery 113 is increased by the converter 111 and is supplied to thefirst inverter 103. The first inverter 103 converts the direct currentvoltage from the battery 113 into an alternating current voltage andsupplies a three-phase current to the electric motor 101. Information onthe SOC and temperature of the battery 113 is inputted into the batteryECU 123 from sensors, not shown. These pieces of information are sent tothe management ECU 119.

The clutch 115 cuts off or connects (cuts off/connects) a driving forcetransmission line from the engine 109 to the drive wheels DW, DW basedon an instruction from the management ECU 119. With the dutch 115engaged, the driving force from the engine 109 is not transmitted to thedrive wheels DW, DW, whereas with the dutch 115 engaged, the drivingforce from the engine 109 is transmitted to the drive wheels DW, DW.

The auxiliary 117 includes, for example, a compressor of an airconditioner for controlling the temperature in a passenger compartment,audio equipment and lamps and operates on electric power supplied fromthe battery 113. The consumed energy by the auxiliary 117 is monitoredby a sensor, not shown, and information on the consumed energy is thensent to the management ECU 119.

The management ECU 119 switches the driving force transmission systemsand controls and monitors the driving of the electric motor 101, thefirst inverter 103, the second inverter 105, the engine 109, and theauxiliary 117. In addition, vehicle speed information from a vehiclespeed sensor, not shown, accelerator pedal opening (AP opening)information of an accelerator pedal, not shown, brake pedal effortinformation of a brake pedal, not shown, and shift range information andinformation from an eco-switch are inputted into the management ECU 119.The management ECU 119 instructs the motor ECU 121, the battery ECU 123,the engine ECU 125 and the generator ECU 127.

The vehicle 1 which is configured in this way can run in various drivemodes based on different drive sources such as, for example, an “EVdrive mode,” a “series drive mode,” and an “engine drive mode” inaccordance with the running conditions of the vehicle. Hereinafter, therespective drive modes in which the vehicle 1 can run will be described.

In the EV drive mode, the electric motor 101 is driven by only electricpower from the battery 113 to thereby drive the drive wheels DW, DW,whereby the vehicle 1 is driven. As this occurs, the engine 109 is notdriven, and the clutch 115 is disengaged.

In the series drive mode, the generator 107 generates electric power bypower from the engine 109, and the electric motor 101 is driven by theelectric power generated by the generator 107 to drive the drive wheelsDW, DW, whereby the vehicle 1 is driven, As this occurs, the clutch 115is disengaged. This series drive mode includes a “battery input/outputzero mode,” a “charging-upon-driven mode,” and an “assist mode.”

In the battery input/output zero mode, electric power generated in thegenerator 107 using the power of the engine 109 is supplied directly tothe electric motor 101 via the second inverter 105 and the firstinverter 103 to drive the electric motor 101, whereby the drive wheelsDW, DW are driven to thereby drive the vehicle 1. Namely, the generator107 generates only electric power which corresponds to a demandedelectric power, and substantially, no electric power is inputted into oroutputted from the battery 113.

In the charging-upon-driven mode, electric power generated in thegenerator 107 using the power of the engine 109 is supplied directly tothe electric motor 101 to drive the electric motor 101, whereby thedrive wheels DW, DW are driven to thereby drive the vehicle 1. At thesame time, the electric power generated in the generator 107 using thepower of the engine 109 is supplied to the battery 113 to charge thebattery 113. Namely, the generator 107 generates electric power morethan the demanded electric power demanded of the electric motor 101.Thus, electric, power corresponding to the demanded electric power issupplied to the electric motor 101, while residual electric power issupplied to the battery 113 to he stored therein.

In case the demanded electric power demanded of the electric motor 101surpasses the electric power that can be generated by the generator 107,the vehicle 1 runs in the assist mode. In the assist mode, the electricpower generated in the generator 107 using the power of the engine 109and the electric power from the battery 113 are both supplied to theelectric motor 101 to drive the electric motor 101, whereby the drivewheels DW, DW are driven to drive the vehicle 1.

In the engine drive mode, the clutch 115 is engaged in response to aninstruction from the management ECU 119, whereby the drive wheels DW, DWare driven directly by the power of the engine 109 to thereby drive thevehicle 1.

In switching these drive modes, a controller for a hybrid vehicleaccording to the embodiment determines which of the EV drive mode andthe series drive mode fits better to the current running condition ofthe vehicle 1 based on the demanded electric power demanded of theelectric motor 101 which corresponds to the demanded driving forcedemanded of the vehicle 1. Then, in the event that the controllerdetermines that the series drive mode fits better than the EV drivemode, the controller starts the engine 109 and switches the drive modefrom the EV drive mode to the series drive mode. Hereinafter, thedetermination on the start of the engine 109 and the control ofswitching the drive modes will be described in detail. FIG. 2 shows adetailed configuration of the controller of the hybrid vehicle shown inFIG. 1.

Firstly, the management ECU 119 calculates a demanded driving force Fdemanded of the electric motor 101 to drive the vehicle based oninformation on accelerator pedal opening, vehicle speed, gear shiftedposition, brake pedal effort (a demanded driving force calculation unit11). Following this, the management ECU 119 calculates a demanded torqueT demanded of the electric motor 101 based on a value obtained bypassing the demanded driving force F obtained through a low-pass filter(MOT demanded torque calculation unit 12).

Next, the management ECU 119 calculates a demanded electric power Pdemanded of the electric motor 101 based on the demanded torque Tdemanded of the electric motor 101, a voltage (a VCU output voltage)which is supplied after having been increased by the converter 111 andthe current revolution speed of the electric motor 101 (MOT revolutionspeed) (an MOT demanded electric power calculation unit 13).

FIG. 3 shows a detailed configuration of the MOT demanded electric powercalculation unit 13. In calculating a demanded electric power demandedof the electric motor 101, the management ECU 119 calculates an MOTshaft output command Which is an output value to be outputted by theelectric motor 101 based on the demanded torque and revolution speed ofthe electric motor 101 (an MOT shaft output command calculation block21). The MOT shaft output command is calculated based on the followingexpression (1).

MOT Shaft Output Command (kW)=MOT Demanded Torque (N)×MOT RevolutionSpeed (rpm)×2π/60   (1)

In addition, the management ECU 119 calculates a loss generated in theelectric motor 101 based on the demanded torque T demanded of theelectric motor 101, the revolution speed of the electric motor 101 andthe VCU output voltage by retrieving a loss map stored in a memory, notshown (a motor loss calculation block 22). This motor loss includesevery loss that is possible to be generated such as switching loss andthermal loss, as well as loss generated in the converter.

Then, the management ECU 119 calculates a demanded electric power Pdemanded of the electric motor 101 which includes electric powercorresponding to the motor loss by adding the motor shaft output commandand the motor loss (a demanded. electric power calculation block 23).

Returning to FIG. 2, the management ECU 119 determines whether or notthe engine 109 is started based on the demanded electric power Pdemanded of the electric motor 101 calculated (an ENG startdetermination unit 14). When there is a start demand for the engine 109(hereinafter, also referred to as an ENG start demand), the managementECU 119 controls the engine 109 and the generator 107 (an ENG-GENcontrol unit 15).

FIG. 4 shows a detailed configuration of the ENG-GEN control unit 15.Firstly, the management ECU 119 calculates an MOT demanded electricpower generation output value which is an output value of electric powerthat is to be generated by the generator 107 for supply of electricpower corresponding to a. demanded electric power demanded of theelectric motor 101 based on the demanded electric power P demanded ofthe electric motor 101 and the voltage (the VCU output voltage) which isincreased by the converter 111 for supply (an MOT demanded electricpower generation output value calculation block 31).

An SOC to be attained (a target SOC) is set for the battery 113, and itis desirable to charge the battery 113 when the current SOC is lowerthan the target SOC. Consequently, the management ECU 119 calculates ademanded charging output value which corresponds to a charge capacitythat is necessary to reach the target SOC based on the current SOC ofthe battery 113 (a demanded charging output value calculation block 32).Then, the management ECU 119 calculates a demanded electric powergeneration output value by adding the MOT demanded electric powergeneration output value and the demanded charging output value (ademanded electric power generation output value calculation block 33).

The management ECU 119 calculates a revolution speed target value forthe engine 109 which corresponds to the demanded electric powergeneration output value calculated by retrieving a BSTC (Brake SpecificFuel Consumption) map in relation to the revolution speed of the engine109 based on the demanded electric power generation output value (an ENGrevolution speed target value calculation block 34). This ENG revolutionspeed target value is a revolution speed Which provides a best fuelconsumption efficiency corresponding to the demanded electric powergeneration output value. However, in the engine 109, a fuel injectionamount is primarily determined according to an intake air amount, andtherefore, it is difficult to control so that the revolution speed ofthe engine 109 coincides with the ENG revolution speed target value.Then, the revolution speed and torque of the generator 107 which isconnected with a crankshaft, not shown, of the engine 109 are controlledby the generator ECU 127 so as to control the amount of electric powerto be generated by the generator 107 to thereby control the revolutionspeed of the engine 109. Consequently, the ENG revolution speed targetvalue is converted into the revolution speed of the generator 107 (a GENrevolution speed conversion block 35), the revolution of the generator107 is controlled (a GEN revolution control block 36), and a GEN torquecommand is sent to the generator ECU 127 (a GEN torque command block37).

The management ECU 119 calculates a torque target value for the engine109 which corresponds to the demanded electric power generation outputvalue by retrieving a BSFC (Brake Specific Fuel Consumption) map inrelation to the torque of the engine 109 based on the demanded electricpower generation output value calculated (an ENG torque target valuecalculation block 38). The management ECU 119 sends an ENG torquecommand to the engine ECU 125 based on this ENG torque target value (aGEN torque command block 39). Then, the management ECU 119 operates athrottle opening based on the torque target value calculated, thecurrent revolution speed of the engine 109 and an intake air amountestimation value based on the torque target value and the currentrevolution speed (a TH opening operation block 40). The management ECU119 performs a DBW (Drive By Wire) control based on the throttle openingcommand calculated (a TH opening command block 41) (a DBW block 42).

Returning to FIG. 2, when no ENG start demand is made by the ENG startdetermination block 14, the engine 109 is not started, and the electricpower in the battery 113 is supplied to the electric motor 101, wherebythe vehicle runs in the EV drive mode. Consequently, the engine 109 andthe generator 107 are not controlled.

Irrespective of the ENG start demand being made, the management ECU 119sends a torque command for the electric motor 101 to the motor ECU 121based on the demanded torque T calculated in the MOT demanded torquecalculation block 11 (an MOT torque command unit 16). The motor ECU 121controls the electric motor 101 based on the MOT torque command.

FIG. 5 shows a detailed configuration of the ENG start determinationunit 14. Here, the management ECU 119 determines that a start demand forthe engine 109 is made when at least one of conditions that will bedescribed later is met (an ENG start demand block 57). Hereinafter, theconditions will be described in detail.

Firstly, when there is made an air conditioning demand such as a demandfor cooling or heating of a passenger compartment, the electric power inthe battery 113 is consumed much, and it is highly possible that theengine 109 needs to be started due to head generated by the engine 109being made use of in heating the passenger compartment. Consequently,when there is made such an air conditioning demand as a demand forcooling or heating the passenger compartment, it is determined thatthere is made a start demand for the engine 109 (an air conditioningdemand determination block 51).

When the SOC of the battery 113 is extremely low, a sufficient outputcannot be obtained from the battery 113, and hence, it is difficult thatthe vehicle runs in the EV drive mode. Thus, it is highly possible thatthe engine 109 is driven to charge the battery 113. Consequently, whenthe SOC of the battery 113 is lower than a predetermined threshold Sth,it is determined that there is made a start demand for the engine 109 (alow SOC determination block 52). In this case, in order to prevent thefrequent occurrence of start and stop of the engine 109, thedetermination is made based on a threshold having a constant hysteresiswidth.

Additionally, when the vehicle is running at a high speed which is equalto or faster than a predetermined speed, the demanded driving forcedemanded of the vehicle is high, and it is difficult that the vehicleruns in the EV drive mode, Thus, it is highly possible that the vehicleruns in the series drive mode by starting the engine 109. Consequently,it is determined that there is made a start demand for the engine 109when the vehicle speed is higher than a predetermined threshold Vth (ahigh vehicle speed determination block 53). In this case, too, in orderto prevent the frequent occurrence of start and stop of the engine 109,the determination is made based on a threshold having a constanthysteresis width,

Even in the event that none of the conditions described above is met, afuzzy determination is performed based on a drive mode fitnessestimation in relation to fuel consumption and anintention-to-accelerate estimation in relation to a driver's intentionto accelerate (a fuzzy determination block 54). When it is determinedfrom the fuzzy determination that the series drive mode is suited betterthan the EV drive mode, it is determined that there is made a startdemand for the engine 109. Hereinafter, the fussy determination will bedescribed in detail.

FIG. 6 shows the drive mode fitness estimation in the fuzzydetermination block 54. Firstly, the management ECU 119 sets anavailable uppermost outputting value P_(U) of the battery 113 and afuel-consumption-reducing output upper limit value P_(L) based the SOCand temperature of the battery 113.

The available uppermost outputting value P_(U) of the battery 113 is anupper limit value of electric power that the battery 113 can supply andvaries according to the SOC and temperature of the battery 113.Consequently, the management ECU 119 calculates maximum electric powersthat the battery 113 can supply based on the SOC and temperature of thebattery 113, respectively. Then, the management ECU 119 sets a smallervalue of the values so calculated as an available uppermost outputtingvalue P_(u) of the battery 113 (an available uppermost outputting valuesetting block 61). Data on maximum electric powers that the battery 113can supply according to the SOC and temperature of the battery 113 areobtained in advance through experiments and are stored in a memory ofthe like, not shown.

In contrast, the fuel-consumption-reducing output upper limit valueP_(L) is a boundary value between a region where a running in the EVdrive mode contributes better to improvement in fuel consumption and aregion where a running in the battery input/output zero drive modecontributes better to improvement in fuel consumption. This value is setby the following method.

In the EV drive mode, the vehicle runs by supplying the electric powerof the battery 113 to the electric motor 101. As this occurs, a loss isgenerated when the direct current voltage of the battery 113 isconverted into the alternating current voltage in the first inverter103, and a loss is also generated when the electric motor 101 is driven.In addition, the SOC of the battery 113 is reduced by supplying theelectric power of the battery 113, The level of the SOC so reduced hereneeds to be returned to the original level sometime in the future bygenerating electric power using the power of the engine 109. A loss isalso generated when the generator 107 generates electric power using thepower of the engine 109 to return the level of the SOC of the battery113 to the original level thereof. Consequently, a total loss L_(EV)which is generated in the EV drive mode is a sum of the loss generatedwhen the electric power is supplied from the battery 113 to the electricmotor 101, the loss generated when the electric motor 101 is driven, andthe loss generated when the generator 107 generates electric powerlater.

In contrast, in the battery input/output zero mode, the generator 107generates only electric power corresponding to the demanded electricpower by a power of the engine 109, and the electric motor 101 is drivenby the electric power so generated, whereby the vehicle runs. Losses aregenerated respectively when the generator 107 generates electric powerby a power of the engine 109 and when the electric motor 101 is driven.Consequently, a total loss L_(SE) generated in the battery output/inputzero mode is a sum of the loss generated when the generator 107generates electric motor and the loss generated when the electric motor101 is driven.

The management ECU 119 calculates output upper limit values of thebattery 113 based on the SOC and temperature of the battery 113,respectively, to such an extent that the total loss L_(EV) generated inthe EV drive mode does not surpass the total loss L_(SE) generated inthe battery input/output zero mode. The management ECU 119 then sets asmaller value of the output upper limit values so calculated as afuel-consumption-reducing output upper limit value P_(L)fuel-consumption-reducing output upper limit setting block 62). Data onthe upper limit values according to the SOC and temperature of thebattery 113 to such an extent that L_(EV) does not surpass the L_(SE)are obtained in advance through experiments and are stored in the memoryof the like, not shown.

FIG. 7 shows the available uppermost outputting value P_(U) and thefuel-consumption-reducing output upper limit value P_(L), In the figure,an axis of abscissas denotes vehicle speed (km/h) and an axis ofordinates denotes driving force (N). Reference character R/L in thefigure denotes a running resistance on the flat ground or road.

Namely, when demanded electric power P>available uppermost outputtingvalue P_(U), that is, in a region (C) in FIG. 7, the demanded electricpower P cannot be supplied by the battery 113 only, Consequently, thevehicle cannot run in the EN drive mode in the region (C), andtherefore, the management ECU 119 controls so that the engine 109 isstarted to thereby enable the vehicle to run in the series drive mode.

When demanded electric power P<fuel-consumption-reducing output upperlimit P_(L), that is, in a region (A) in FIG. 7, the demanded electricpower P is not so large, and hence, the consumption of electric power atthe battery 113 is also not so large. In addition, the electric powerthat is to be generated later is also not so large. Consequently, lossesgenerated respectively are also not so large, resulting inL_(EV)<L_(SE). Consequently, in the region (A), it is preferable thatthe vehicle runs in the EV drive mode from the viewpoint of fuelconsumption, and therefore, the management ECU 119 controls so that thevehicle runs in the EV drive mode without starting the engine 109.

When fuel-consumption-reducing output upper limit P_(L)≦demandedelectric power P≦available uppermost outputting value P_(U), namely, ina region (B), since the demanded electric power P does not surpass theavailable uppermost outputting value P_(U), the demanded electric powerP can be supplied by only the electric power of the battery 113, andtherefore, the vehicle can run in the EV drive mode. Since the demandedelectric power P is relatively large, however, the consumption ofelectric power at the battery 113 also becomes relatively large, andadditionally, an electric power to be generated later also becomeslarge, thereby resulting in L_(EV)≧L_(SE). Because of this, in theregion (B), it is desirable that the vehicle runs in the series drivemode from the viewpoint of fuel consumption. However, starting theengine 109 immediately after demanded electric power P≧P_(L) causesfears that the control is switched frequently. Then, whenfuel-consumption-reducing output upper limit P_(L)≦demanded electricpower P≦available uppermost outputting value P_(U), the management ECU119 performs a fussy reasoning.

Returning to FIG. 6, the management ECU 119 sets a drive mode fitnessestimation membership function from the available uppermost outputtingvalue P_(U) and the fuel-consumption-reducing output upper limit valueP_(L) of the battery 113. Then, a fitness of the drive mode to thecurrent demanded electric power P is calculated from the followinglanguage control rules (a drive mode's fitness calculation block 63).

<Language Control Rules>

(1) If MOT demanded electric power is smaller than P_(L), the seriesdrive mode fitness is high, and(2) If MOT demanded electric power is larger than P_(U), the seriesdrive mode fitness is low.

FIG. 8 shows of an intention-to-accelerate estimation in the fuzzydetermination block 54. Firstly, the management ECU 119 calculates adifferential value of an accelerator pedal opening AP Then, themanagement ECU 119 calculates an accelerator pedal opening temporalchange rate ΔAP (a ΔAP calculation block 71), Then, anintention-to-accelerate estimation value for the current ΔAP iscalculated from an intention-to-accelerate estimation membershipfunction regarding a predetermined ΔAP and the following languagecontrol rules (an intention-to-accelerate estimation value calculationblock 72). Note that values p, q are set as demanded throughexperiments.

<Language Control Rules>

(1) if ΔAP is smaller than p, the intension to accelerate is small, and

(2) If ΔAP is larger than q, the intension to accelerate is large.

FIG. 9 shows a calculation of a degree of ENG start demand by the fuzzydetermination block 54. The management ECU 119 calculates barycenters ofthe drive mode fitness and the intension to accelerate estimation value(a barycenter calculation block 81) and calculates a degree of ENG startdemand (a degree-of-ENG-start-demand calculation block 82). This degreeof ENG start demand has an arbitrary value between −1 to 1.

Returning to FIG. 5, the management ECU 119 integrates the degree of ENGstart demand calculated by the fuzzy determination block 54 (anintegration block 55). The integration of the degree of ENG start demandis executed so as to obtain a value in the range of 0 to 1. En the eventthat the integral value so calculated is higher than a predeterminedthreshold Ith, it is determined that there is made a start demand forthe engine 109 (an integral value determination block 56). In this case,too, in order to prevent the frequent occurrence of start and stop ofthe engine 109, the determination is made based on a threshold having apredetermined hysteresis width, By utilizing the integral value of thedegree of ENG start demand, it can be determined that there is made astart demand for the engine 109 only when the fluctuation in demandedelectric power or accelerator pedal opening is not temporary but iscontinuous. Therefore, it is possible to prevent the frequent occurrenceof start and stop of the engine 109 in an more ensured fashion.

Hereinafter, the operation of the controller for a hybrid vehicleaccording to the embodiment will be described in detail, FIG. 10 showsoperations of the controller for the hybrid vehicle 1 according to theembodiment. Firstly, the management ECU 119 calculates a demandeddriving force F demanded of the electric motor 101 (step S1) and thencalculates a demanded torque T demanded of the electric motor 101 (anMOT demanded torque) based on the demanded driving force F (step S2).Following this, the management ECU 119 calculates a demanded electricpower P demanded of the electric motor 101 (an MOT demanded electricpower) based on the MOT demanded torque T, the MOT revolution speed andthe VCU output voltage (step 53). The management ECU 119 makes, based onthis MOT demanded electric power P, a determination on whether or notthe engine 109 is started (an ENG start determination) (step S4).

FIG. 11 shows operations of the ENG start determination. In determiningwhether or not the engine 109 is started, the management ECU 119determines whether or not there is made an air conditioning demand suchas a demand for cooling or heating the passenger compartment (step S11).If it determines that there is made no air conditioning demand, themanagement ECU 119 determines whether or not the SOC of the battery 113(the battery SOC) is lower than the predetermined threshold Sth (stepS12).

If it determines in step S12. that the battery SOC Sth, the managementECU 119 determines whether or not the vehicle speed is higher than thepredetermined threshold Vth (step S13). In order to prevent the frequentoccurrence of switching in control, these thresholds Sth. Vth are set soas to have predetermined hysteresis widths. If the vehicle speed Vth,the management ECU 119 executes a fuzzy determination (step S14).

If it determines in step S11 that there is made an air conditioningdemand, if it determines in step 512 that the battery SOC<Sth, or if itdetermines in step S13 that the vehicle speed>Vth, understanding thatthere is an ENG start demand, the management ECU 119 executes thefollowing operation (step S15).

FIG. 12 shows operations of the fuzzy determination which is executedduring the ENG start determination. Firstly, the management ECU 119calculates an available uppermost outputting value P_(U) and afuel-consumption-reducing output upper limit value P_(L) based on theSOC and temperature of the battery 113 (step S21). Then, the managementECU 119 determines whether or not the demanded electric power P demandedof the electric motor 101 is larger than the available uppermostoutputting value P_(U) (step S22). If it determines that the demandedelectric power P demanded of the electric motor 101≧P_(U), themanagement ECU 119 determines whether or not the MOT demanded electricpower P is smaller than the fuel-consumption-reducing output upper limitvalue P_(L). (step S23). If it determines in step S23 that the demandedelectric. power P demanded of the electric motor101≦fuel-consumption-reducing output upper limit value P_(L),understanding that there is made no ENG start demand, the management ECU119 ends the fuzzy determination.

If it determines in step S23 that the demanded electric power P demandedof the electric motor 101≧the fuel-consumption-reducing output upperlimit value P_(L), that is, the fuel-consumption-reducing output upperlimit P_(L)≦the MOT demanded electric power P≦the available uppermostoutputting value P_(U), the management ECU 119 sets a drive mode fitnessestimation membership function from the fuel-consumption-reducing outputupper limit P_(L) and the available uppermost outputting value P_(U).Then, the management ECU 119 executes a fuzzy reasoning based on thedrive mode fitness estimation membership function and the currentdemanded electric power P demanded of the electric motor 101 so as tocalculates a fitness of the drive mode to the current demanded electricpower P demanded of the electric motor 101 (step S24).

Next, the management ECU 119 executes a fuzzy reasoning based on theintention-to-accelerate estimation membership function in relation tothe accelerator pedal opening temporal change rate ΔAP and the currentΔAP is calculated from so as to calculate an intention-to-accelerateestimation value for the current ΔAP (step S25), Then, the managementECU 119 calculates barycenters of the drive mode fitness and theintension to accelerate estimation value so as to calculate a degree ofENG start demand (step S26).

Next, the management ECU 119 integrates the degree of ENG start demand(step S27). Then, the management ECU 119 determines whether or not theintegral value of the degree of ENG start demand is equal to or largerthan a predetermined threshold Ith. In order to prevent the frequentoccurrence of switching in control, the threshold Ith is set so as tohave a predetermined hysteresis width. If it determines in step S27 thatthe integral value<Ith, understanding that there is made no ENG startdemand, the management ECU 119 ends the fuzzy determination. If itdetermines in step S22 that the demanded electric power P demanded ofthe electric motor 101>P_(U), or if it determines in step S28 that theintegral value≧Ith, understanding that there is made an ENG startdemand, the management ECU 119 executes the next operation.

Returning to FIG. 10, the management ECU 119 determines based on theENG. start determination in step S4 whether or not there has been madean ENG start demand (step S5). If it determines in step S5 that therehas been made no ENG start demand, the management ECU 119 controls theelectric motor 101 based on the demanded torque T so as to cause thevehicle to run in the EV drive mode without starting the engine 109(step S7). In contrast, if it determines in step S5 that there has beenmade an ENG start demand, the management ECU 119 controls the engine 109and the generator 107 so as to cause the vehicle to run in the seriesdrive mode by starting the engine 109 (step S6). At the same time, themanagement ECU 119 controls the electric motor 101 based on the demandedtorque T (step S7).

Thus, according to the controller for a hybrid vehicle of thisembodiment, the engine 109 is started when the available uppermostoutputting value P_(U) which is set according to the conditions of thebattery 113 surpasses the demanded electric power of the electric motor101, and therefore, not only can the desired demanded electric power beensured, but also the over charge of the battery 113 can be prevented.Additionally, the fuel-consumption-reducing output upper limit valueP_(L) is set which is the maximum value of the demanded electric powerwith which the fuel consumption resulting when the vehicle runs in theEV drive mode is improved better than the fuel. consumption resultingwhen the vehicle runs in the battery input/output zero mode, and it isdetermined based on the fuel-consumption-reducing output upper limitvalue P_(L) whether or not the engine 109 is started. Therefore, thefuel consumption can be improved further. In addition, thefuel-consumption-reducing output upper limit value P_(L), is set basedon the conditions of the battery 113 in consideration of the fact thatthe outputting electric power is reduced depending upon the SOC andtemperature of the battery 113, and therefore, the over charge of thebattery 113 can be prevented.

Additionally, according to the controller for a hybrid vehicle of theembodiment, when the demanded electric power demanded of the electricmotor 101 is somewhere between the fuel-consumption-reducing outputupper limit value P_(L) and the available uppermost outputting valueP_(U), the fuzzy reasoning is executed based on the demanded electricpower demanded of the electric motor 101 and the driver's intention toaccelerate, whereby it is determined based on the results of the fuzzyreasoning whether or not the engine 109 is started. This not only caneliminate fears that the lack of driving force is caused by theinsufficient output of the battery 113 but also can prevent the electricmotor 101 from performing unnecessary operations of the engine 109.Additionally, the continuity of the running condition of the vehicle canbe determined by integrating the degree of ENG start demand, andtherefore, the unnecessary operation of the engine 109 is obviated, Byso doing, a more accurate control reflecting the intention of the drivercan be executed.

FIRST MODIFIED EXAMPLE

In the embodiment, the management ECU 119 set the drive mode fitnessestimation membership function based on the SOC and temperature of thebattery 113. However, the drive mode fitness estimation membershipfunction can. be corrected based on the temperature of the coolant ofthe engine 109 or the consumed electric power of the auxiliary 117.

For example, when the temperature of the coolant of the engine 109 islow, it is highly possible that the warming up of the engine 109 needsto be promoted, and therefore, it is desirable that the vehicle runs inthe series drive mode by starting the engine 109 earlier. Consequently,when the temperature of the coolant of the engine 109 is low, the drivemode fitness estimation membership function is corrected so that a highfitness to the series running tends to be calculated easily. When thetemperature of the coolant of the engine 109 is lower than apredetermined value, this correction is implemented by utilizing anarbitrary method such as a method of subtracting a predetermined valuefrom the fuel-consumption-reducing output upper limit value P_(L) or amethod of subtracting a value corresponding to the temperature of thecoolant of the engine 109 from the fuel-consumption-reducing outputupper limit value P_(L). By correcting the drive mode fitness estimationmembership function in this way, it becomes easy to make a determinationthat there is made a demand for starting the engine 109 when thetemperature of the coolant of the engine 109 is low.

Additionally, when the temperature of the coolant of the engine 109 ishigh, it is highly possible that the engine 109 needs to be inoperativeso as to reduce the temperature of the coolant, and therefore, it isdesirable that the vehicle runs in the EV drive mode without startingthe engine 109. Consequently, when the temperature of the coolant of theengine 109 is high, the drive mode fitness estimation membershipfunction is corrected so that a low fitness to the series running tendsto be calculated easily. When the temperature of the coolant of theengine 109 is higher than a predetermined value, this correction isimplemented by utilizing an arbitrary method such as a method of addinga predetermined value to the fuel-consumption-reducing output upperlimit value P_(L) or a method of adding a value corresponding to thetemperature of the coolant of the engine 109 to thefuel-consumption-reducing output upper limit value P_(L). By correctingthe drive mode fitness estimation membership function in this way, itbecomes difficult to make a determination that there is made a demandfor starting the engine 109 when the temperature of the coolant of theengine 109 is high, so that it becomes easy to continue the EV drivemode.

Additionally, when the consumed electric power by the auxiliary 117 islarge, it is preferable to start the engine 109 earlier so as to chargethe battery 113. Consequently, when the consumed electric power by theauxiliary 117 is large, the drive mode fitness estimation membershipfunction is corrected so that a high fitness to the series drive mode iscalculated. When the consumed electric power by the auxiliary 117 islower than a predetermined value, this correction is implemented byutilizing an arbitrary method such as a method of subtracting apredetermined value from the fuel-consumption-reducing output upperlimit value P_(L) or a method of subtracting a value corresponding tothe consumed electric power of the auxiliary 117 from thefuel-consumption-reducing output upper limit value P_(L). By so doing,the drive mode fitness estimation membership function is corrected, sothat it becomes easy that the high degree of ENG start demand iscalculated, Therefore, the engine 109 can be started earlier to generateelectric power, thereby making it possible to ensure the demandedelectric power.

SECOND MODIFIED EXAMPLE

In the embodiment described above, the management ECU 119 sets theintention-to-accelerate estimation membership function based on theaccelerator pedal opening temporal change rate ΔAP. However, theintention-to-accelerate estimation membership function can be correctedbased on the eco-switch by which priority is given to fuel consumptionor setting of a gearshift range.

For example, when the eco-switch is on, it is determined that the driverdesires a running in which priority is given to fuel consumption, andtherefore, it is preferable that the vehicle runs in the EV drive modewithout starting the engine 109. Consequently, when it is determinedthat the driver is determined to desire the running in which priority isgiven to fuel consumption, the intention-to-accelerate estimationmembership function is corrected positively so that the sensitivity ofthe intention-to-accelerate determination is decreased.

In addition, when the gearshift range is set to a sports mode, it isdetermined that the driver desires a running in which priority is givento acceleration. Therefore, it is desirable that the vehicle runs in theseries drive mode by starting the engine 109 earlier. Consequently, whenit is determined that the driver desires the running in which priorityis given to acceleration, the intention-to-accelerate estimationmembership function is corrected negatively so that the sensitivity ofthe intention-to-accelerate determination is increased. By correctingthe intention-to-accelerate estimation membership function in this way,the driveability can be improved by taking the intention of the driverinto consideration, Additionally, the fuel consumption can be improvedfurther.

THIRD MODIFIED EXAMPLE

In the embodiment described above, depending upon the running conditionsof the vehicle, there may be a situation in which the loss becomessmaller when the vehicle runs in the engine drive mode in which thedrive wheels DW, DW are directly driven by the engine 109 than when thevehicle runs in the series drive mode. In this case, the management ECU119 engages the clutch 115 so as to switch the drive mode from theseries drive mode to the engine drive mode, whereby the vehicle can bedriven with good efficiency.

In the engine drive mode, the engine 109 is connected to the driveshafts of the drive wheels DW, DW by engaging the clutch 115. When theengine 109 is connected to the drive wheels DW, DW, the engine 109cannot be run at an operation point which provides good fuel consumptiondue to the limit to setting of the gear ratio, generating the loss. Inaddition, a mechanical loss is also generated.

On the other hand, in the battery input/output zero mode, although theengine 109 can be run at an operation point which good fuel consumption,an electrical loss is generated somewhere along the supply line ofsupplying the electric power generated by the generator 107 to theelectric motor 101 via the second inverter 105 and the first inverter103.

Then, in the third modified example, a total loss that would begenerated in the engine drive mode and a total loss that would begenerated in the battery input/output zero mode are obtained in advancethrough experiments. Then, when the total loss generated in the enginedrive mode becomes smaller than the total loss generated in the batteryinput/output zero mode, that is, when it is determined that the fuelconsumption becomes better when the vehicle runs in the engine drivemode than when the vehicle runs in the series drive mode, the managementECU 119 engages the clutch 115, so that the vehicle runs in the enginedrive mode. By so doing, the drive mode can quickly be shifted from theseries drive mode to the engine drive mode, and therefore, the fuelconsumption can be improved further.

Note that the invention is not limited to the embodiment but can bemodified or improved as required.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

101 Electric motor (MOT); 107 Generator (GEN); 109 Multi-cylinderinternal combustion engine (ENG); 113 Battery (BATT); 115 Lockup clutch;117 Auxiliary (ACCESSORY); 119 Management ECU (MG ECU)

1. A controller for a hybrid, the vehicle including an engine, anelectric motor, a generator for generating electric power by power ofthe engine, and a battery for storing electric power generated by theelectric motor or the generator and supplying the electric power to theelectric motor, the vehicle being able to run in an EV drive mode inwhich the electric motor is driven by electric power of the battery onlyand a series drive mode in which the electric motor is driven byelectric power generated by the generator using power of the engine, thecontroller including a demanded driving force calculation unit forcalculating a demanded driving force for the electric motor based onvehicle speed and accelerator pedal opening, a demanded electric powercalculation unit for calculating a demanded electric power based on thedemanded driving force and a revolution speed of the electric motor, anavailable uppermost outputting value setting unit for setting anavailable uppermost outputting value for the battery based on theconditions of the battery, and an engine starting determination unit fordetermining on the starting of the engine based on the demanded electricpower, wherein the engine starting determination unit starts the engineso that the vehicle runs in the series drive mode when the demandedelectric power exceeds the available uppermost outputting value.
 2. Thecontroller of claim 1, wherein the series drive mode includes a batteryinput/output zero mode in which only electric power corresponding to thedemanded electric power is generated by the generator for supply to theelectric motor, wherein the controller further includes a set valuesetting unit for setting a set value based on the conditions of thebattery, wherein the set value is a smaller value than the availableuppermost outputting value and is an upper limit value for an outputwhich satisfies {(Loss generated when running in EV drive mode)+(Lossgenerated when generating electric power corresponding to electric powerconsumed in EV drive mode)}<(Loss generated in battery input/output zeromode), and wherein the engine starting determination unit starts theengine in accordance with the running conditions of the vehicle so as tocause the vehicle to run in the series drive mode when the demandedelectric power is equal to or larger than the set value and is equal toor smaller than the available uppermost outputting value.
 3. Thecontroller of claim 2, wherein the available uppermost outputting valueand the set value are set based on the state-of-charge of the battery orthe temperature of the battery.
 4. The controller of claim 2, whereinthe available uppermost outputting value and the set value are set basedon a smaller value of values which are calculated based on thestate-of-charge of the battery and the temperature of the battery. 5.The controller of claim 2, wherein the available uppermost outputtingvalue and the set value are set smaller as the state-of-charge of thebattery becomes smaller.
 6. The controller of any one of claims 2 to 5claim 2, wherein the available uppermost outputting value and the setvalue are set smaller as the temperature of the battery becomes smaller.7. The controller of claim 2, further a first fitness calculation unitfor calculating a first fitness between the available uppermostoutputting value and the set value by executing a fuzzy reasoning from afirst membership function which is set with respect to demanded electricpower, a second fitness calculation unit for calculating a secondfitness by executing a fuzzy reasoning from a second membership functionwhich is set with respect to variation in accelerator pedal opening, anda degree-of-start-demand calculation unit for calculating a degree ofstart demand for the engine based on the first fitness and the secondfitness, wherein the engine starting determination unit starts theengine and causes the vehicle to run in the series drive mode when anintegral value obtained by integrating the degree of start demandsurpasses a predetermined value, with the demanded electric power beingequal to or larger than the set value and being equal to or smaller thanthe available uppermost outputting value.
 8. The controller of claim 7,wherein the first membership function is corrected in accordance withthe temperature of a coolant of the engine,
 9. The controller of claim7, wherein the first membership function is corrected in accordance withenergy which is consumed by an auxiliary.
 10. The controller of claim 7,further including an intention-to-accelerate determination unit fordetermining on a driver's intention to accelerate, wherein the secondmembership function is positively corrected when theintention-to-accelerate determination unit determines that the driver'sintention to accelerate is high, whereas the second membership functionis corrected negatively when the intention-to-accelerate determinationunit determines that the driver's intention to accelerate is low. 11.The controller of claim 2, wherein the vehicle can run in an enginedrive mode in which drive wheels are driven by power of the engine byengaging a clutch which is provided between the engine and the electricmotor, wherein the controller further includes a clutchengaging/disengaging unit for engaging and disengaging the clutch, andwherein the clutch engaging/disengaging unit engages the clutch tochange the drive modes from the series drive mode to the engine drivemode when a loss generated in the series drive mode is larger than aloss generated in the engine drive mode.